1. Field of the Invention
The present invention relates to methods of producing a metal-clad laminate. More particularly, the present invention is relates to methods of producing a circuit board which uses the obtained metal-clad laminate.
2. Discussion of the Background
Metal-clad laminates and circuit boards widely used for various electronic equipments are required to achieve thinning of each layer and fine wiring of circuit so as to provide downsized and high-functional electronic equipments. A metal-clad laminate is generally produced by laying one or plural sheets of prepreg, sandwiching same with copper foil, pressing and heating them under reduced pressure using a vacuum hot press machine to achieve lamination and integration. Then, a circuit board is widely prepared by forming a circuit on the thus-produced metal-clad laminate by a subtractive method using a copper foil as a conductor layer. To ensure close adhesion between the conductor layer and the prepreg layer, however, concave and convex need to be formed in the interface between the conductor layer (i.e., copper foil of metal-clad laminate) and the prepreg layer. However, when such concave and convex are formed on a conductor layer, a conductor layer in the concave and convex part of an unnecessary conductor layer to be removed by etching during circuit formation is not easily removed, and when etching is performed under conditions enabling sufficient removal of a conductor layer in the concave and convex part, a necessary conductor layer (wiring pattern to be a circuit) is problematically fused markedly, thus preventing fine wiring.
As a method for solving such a problem, a method including transferring a metal film layer capable of forming a plating seed layer onto an adhered by using a film with a metal film such as copper foil with ultra-thin metal and the like has been tried (see, e.g., JP-A-2004-230729 and JP-A-2002-324969).
The method including transferring a metal film layer capable of forming a plating seed layer onto an adhered by using a film with a metal film is considered to be an advantageous method for fine wiring, since it enables smooth formation of a conductor layer on an insulating layer. On the other hand, production of a circuit board using a metal-clad laminate is associated with the problem of susceptibility of the transferred metal film layer to damage, since a through hole formation step and a desmearing step are present before formation of a conductor layer. For example, when a desmear treatment is performed by a treatment with an oxidizer such as alkaline potassium permanganate solution and the like, a neutralization treatment with an acidic solution is necessary, during which a copper film may be damaged. Moreover, a copper film may be damaged during a pretreatment of a copper film with an acidic solution for the formation of a conductor layer by electroplating.